The present invention relates to complementary metal oxide semiconductor (CMOS) image sensors and methods of forming the same, and more particularly, to CMOS image sensors including active pixel regions and optical black regions, and methods of forming the same.
A complementary metal oxide semiconductor (CMOS) image sensor is an element that converts optical images to electrical signals. CMOS image sensors with improved performance are increasingly desired for various applications, such as digital cameras, camcorders, personal communication systems (PCS), game consoles, security cameras, medical micro cameras, robots, and the like.
A unit pixel in a CMOS image sensor includes a photoelectric converter and a charge transfer unit. The charge transfer unit transfers, to a charge detector, electric charges that the photoelectric converter generates by photoelectrically converting incident light.
In the course of fabricating a CMOS image sensor, etching and ion implantation operations are repeatedly performed on a semiconductor substrate. These repeated operations may cause damage to silicon-oxygen bonds on the surface of the semiconductor substrate, thereby generating dangling bonds of —Si—O— or —Si—. The dangling bonds may reduce dark current, which flows from a photoelectric converter to a charge transfer unit, which may cause the reliability of a CMOS image sensor to deteriorate. To remove the dangling bonds, hydrogen may be diffused into the semiconductor substrate. To diffuse hydrogen, a passivation layer may be formed on the substrate and an annealing operation may be carried out.
A CMOS image sensor includes an active pixel region and an optical black region. The active pixel region receives incident light and converts the light into an electrical signal, and the optical black region blocks incident light to provide a standard for a black (i.e. no light) signal on the active pixel region. In the optical black region, the light shield layer that is formed to intercept incident light may also limit or prevent hydrogen diffusion into the semiconductor substrate during the hydrogen annealing operation. Due to the presence of the light shield layer, dangling bonds can be removed from the active pixel region, but may not be removed from the optical black region. Thus, signals output from the active pixel region and the optical black region may be different from each other, which may decrease the reliability of the CMOS image sensor.